Railroad locomotives typically use a pneumatic braking system controlled by an independent brake (that is separate from the train brakes). The locomotive may include a dynamic braking system whereby the traction motors are reversed so that they generate braking power which is commonly dissipated in a large resistive grid on the locomotive.
U.S. Pat. No. 6,027,181 discloses a system for a locomotive which includes a blended braking system combining a pneumatic braking system for the train with a dynamic braking system on the locomotive.
The present inventors have disclosed a system for controlling a dynamic and regenerative braking system for a hybrid locomotive which employs a control strategy for orchestrating the flow of power amongst the prime mover, the energy storage system and the regenerative braking system in a U.S. Patent Application Publication Number 2006-0076171 filed Aug. 9, 2005 entitled “Regenerative Braking Methods for a Hybrid Locomotive” which is also incorporated herein by reference.”
As presented in U.S. Patent Application Publication Number 2006-0076171, the concept was to recover energy from the traction motors to either dissipate this power in resistive grids (dynamic braking) and/or feed this power into a DC bus if the DC bus is equipped with any means of energy storage, such as for example, a battery pack, a capacitor bank and/or a flywheel system. As shown in FIG. 23 of U.S. Patent Application Publication Number 2006-0076171, the proposed method consists in reversing the power flow of the armature and field windings in series to switch from the motoring to braking mode. In this configuration with both windings in series, it may be difficult to control the power drawn from the traction motors in braking mode.
In U.S. patent application Ser. No. 11/200,881 filed Aug. 9, 2005 entitled “Locomotive Power Train Architecture”, Donnelly et al. have further disclosed a general electrical architecture for locomotives based on a plurality of power sources, fuel and drive train combinations. The power sources may be any combination of engines, energy storage and regenerative braking. This application is also incorporated herein by reference.
In rail yard switching operations, for example, a locomotive may be operated primarily at low speed (speeds less than about 15 mph) with multiple stop and starts. In these situations, the braking system is worked hard and is a high maintenance system on the locomotive. Further, if the brake system locks up, it can cause wheel skid which can result in flat spots developing on the skidding wheels. Flat spots are a further costly high maintenance operation usually requiring wheel replacement.
There thus remains a need for a locomotive braking system that can be used in conjunction with or instead of a mechanical or pneumatic locomotive braking system, that is particularly suited for operations at low speed.
These and other needs are addressed by the various embodiments and configurations of the present invention which are directed generally to utilizing the locomotive's traction motors to return energy from braking to a least one of the locomotive's diesel engines, DC electrical bus, energy storage system or dynamic braking system in a way that minimizes wheel skid and in a way that provides seamless braking action at or near 0 mph.